Chelating (pyrazolylmethyl)pyridine ligands: Coordination chemistry and binding properties with zinc(II) and cadmium(II) cations

Reactions of 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L2) and 2-(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine (L3) with either Zn(NO3) or Cd(NO3) produced monometallic complexes [Zn(NO3)2(L2)] (1), [Zn(NO3)2(L3)] (2), [Cd(NO3)2(L2)] (3) and [Cd(NO3)2(L3)] (4). In the solid state structures of complexes 1, 3 and 4, L2 and L3 ligate to the zinc and cadmium atoms in a bidentate fashion. The pyrazolyl compounds 2-(pyrazol-1-ylmethyl)pyridine (L1), (L2) and (L3) were also used as model chelating agents for liquid–liquid removal of zinc(II), cadmium(II) and lead(II) cations from water using dichloromethane as the organic solvent. L1–L3 showed extraction efficiencies of 70–88% for zinc(II), 50–55% for lead(II) and (19–31%) for cadmium(II). Theoretical results obtained from density functional theory calculations were consistent with the experimental extraction trends.

The 2-(pyrazolylmethyl)pyridine compounds when reacted with either Zn(NO3) or Cd(NO3) form monometallic complexes in which the nitrates are either bidentate or anisodentante depending on the identity of the metal center. The ligands are potential chelating agents for the removal of zinc(II), cadmium(II) and lead(II) metals from water.Figure optionsDownload as PowerPoint slideHighlights
► (Pyrazolylmethyl)pyridine Zn(II) and Cd(II) complexes have been synthesized.
► Cd(II) complexes exhibit higher coordination numbers than Zn(II) complexes.
► The ligands show greater affinities towards Zn(II) in liquid–liquid extractions.
► Steric factors influence the extraction efficiency of the chelating agents.